Melt stabilized polyesters containing aminobenzophenones



United States Patent US. Cl. 260-453 6 Claims ABSTRACT OF THE DISCLOSUREA thermal stabilized polyester composition comprising a saturated linearpolyester and a thermal stabilizer selected from those represented bythe formula wherein R and R are lower alkyl radicals having from 1 to 6carbon atoms.

This invention relates to highly polymeric saturated linear polyesterresins that possess improved thermal stability and to a method ofproducing same.

Saturated linear polyester resins can be prepared by first carrying outa condensation reaction between a suitable dicarboxylic acid or esterthereof with a diol to form a prepolymer. The resulting prepolymer isthen polycondensed to form the desired polyester resin. When an ester ofa dicarboxylic acid is used as the starting material, it is firstreacted with a diol in the presence of a transesterification orester-interchange catalyst by means of an ester-interchange reaction;whereas when a dicarboxylic acid is used as the starting material, it isfirst subjected to a direct esterification reaction with a diol in thepresence of what is generally called a first stage additive or etherinhibitor. In either instance, the resulting reaction product, which maybe generally described as a polyester prepolymer, is then polycondensedin the presence of a polycondensation catalyst to form a polyesterresin.

For example, in the case of the transesterification method of preparingpolyethylene terephthalate, ethylene glycol is reacted with dimethylterephthalate to form a polyester prepolymer which is comprised mainlyof his- 2-hydroxyethyl terephthalate; or in the direct esterificationmethod, ethylene glycol is reacted with terephthalic acid to form theresulting polyester prepolymer which is then polycondensed to form thedesired polyester resin.

Saturated linear polyester resins, such as polyethylene terephthalateand many others, are widely used in the production of films and fibersand the like. However, it is generally known that such polyesterproducts degrade when exposed to heat for a substantial period of time.Such degradation is particularly a problem in the extrusion and spinningprocesses of the finished resins to form the above-denoted products.Additionally, the fibers produced from such resins are extensively usedin the textile field and, as a result of this application, are subjectedto rather extreme temperatures in the processes of washing, drying, andironing. Therefore, it is highly desirable that the polyester resincomposition possess as much stability at high temperatures as possible.

Therefore, it is an object of the present invention to prepare a highlypolymeric saturated linear polyester resin composition which exhibitsimproved thermal stability.

Another object of the present invention is to provide a method ofpreparing saturated linear polyester resin exhibiting such a high degreeof thermal stability.

These and other objects are accomplished in accordance with the presentinvention with a stabilized polyester 3,510,450 Patented May 5, 1970composition comprising a saturated linear polyester containing astabilizing amount of a thermal stabilizer selected from thoserepresented by the formula wherein R and R are lower alkyl radicalshaving from 1 to 6 carbon atoms.

Among the compounds which can be used as thermal stabilizers in thepresent compositions are, for example. 4,4tetramethyldiaminobenzophenone 4,4 tetraamyldiaminobenzophenone, 4dibutylamino-4-dimethylaminobenzophenone,4,4-tetrapropyldiaminobenzophenone, and4-propylethylamino-4-propylethylaminobenzophenone.

The saturated linear polyester resins used in the preparation of thesubject thermal stabilized polyester compositions can be prepared viaeither the conventional ester-interchange reaction or by the directesterification method, both of which are thoroughly disclosed throughoutthe prior art.

In the practice of the present invention, the aboveidentified thermalstabilizers can be incorporated in the resin composition at variousstages. For example, in the preparation of polyester resin, the presentthermal stabilizers can be suitably mixed in the polyester resinreactants before commencing the reaction, or at any stage after theinitial reaction has begun, if indicated. However, in most instances, ithas been found that it is preferred to mix or blend the present thermalstabilizers in the polyester resin immediately after thepolycondensation step has been completed, while the resin is stillmolten.

It has been found that the present benzophenone derivative thermalstabilizers are effective as such in polyester resin compositions whenemployed in amounts ranging from about 0.01% to about 0.5%, by weight,based on the weight of the saturated linear polyester resin. Usually, ithas been found that concentrations ranging from about 0.02% to about0.3%, by weight, are preferred in most instances. However, whenindicated, concentrations less or greater than the above can be used,but their effectiveness is generally reduced proportionall The followingexamples will further serve to illustrate the present invention,although it will be understood that these examples are included merelyfor the purpose of illustration and are not intended to limit the scopeof the present invention. All parts are by weight, unless otherwiseindicated.

I EXAMPLE I A blended mixture comprising 474 g. of terephthalic acid,288 mls. of ethylene glycol and 149 mls. of triethylamine was chargedinto a reaction vessel equipped with a nitrogen inlet, a Dean-Starkeseparating apparatus, heating means and stirring means. The reactionmixture was agitated and the temperature was raised to about 197 C.under a nitrogen blanket at atmospheric pressure. At about C., awater-triethylamine azeotropic mixture started to distill off. Theazeotropic mixture was continuously separated by means of theDean-Starke apparatus, and the triethylamine recovered was continuouslyreturned to the reaction vessel. The reaction mixture became almostclear. Then, the temperature was allowed to rise to about 230 C. over aone-hour period to remove all the t'riethylamine and any excess glycol.The prepolymer product was allowed to cool under an atmosphere ofnitrogen.

EXAMPLE II Fifty grams of the prepolymer product of Example I was mixedwith 0.02 g. of antimony sec-butoxide and placed in a reaction vessel.The reaction mixture was heated at about 280 C. under reduced pressureof from about 0.05 to about 0.1 mm. of mercury while under agitation forabout 2 hours to bring about the polycondensation of the polyesterprepolymer and formation of a olyester resin. The polyethyleneterephthalate resin formed had an original intrinsic viscosity of 0.88,a degraded intrinsic viscosity of 0.69', and the percentage broken bondswas calculated as 0.132.

EXAMPLE III Fifty grams of the prepolymer product of Example I was mixedwith 0.02 g. of antimony sec-butoxide and placed in a reaction vessel.The reaction mixture was heated at about 280 C. under reduced pressureof from about 0.05 to about 0.1 mm. of mercury while under agitation forabout 2 hours to bring about the polycondensation of the prepolymer andformation of a polyester resin. After the polycondensation reaction hadbeen comleted, 0.02 g. of 4,4'-tetramethyldiaminobenzophenone wasthoroughly stirred into the polyester resin while sti l molten atatmospheric pressure, after which the resin product was cooled. Theresulting polyethylene terephthalate resin composition had an originalintrinsic viscosity of 0.59, a degraded intrinsic viscosity of 0.53, anda percentage broken bonds value calculated as 0.081.

In the above examples, the original intrinsic viscosity values of thepolyester resin products were obtained by measuring the intrinsicviscosities of the resin compositions as produced.

The degraded intrinsic viscosity values were determined by the followingprocedure: The polyester resin composition was ground and passed througha 10' USS. mesh screen and dried at 120 C. in vacuo for 1 6 hours, thencooled in a desiccator. Two to three grams of this dried resin was thenplaced in a test tube which was then inserted into an aluminum blockpreheated to 280 C. (10.5 C.). The block was then sealed and evacuatedto 0.1 mm. of mercury. After holding for about 10-15 seconds, the blockwas filled with dried, oxygen-free nitrogen gas. This vacuum-nitrogenpurge was then repeated for a total of three times; the entire processtook -7 minutes. Then, the resin sample was left in the heated block foran additional two hours under a slow stream of nitrogen. After thistwo-hour period, the resin sample was removed from the block and placedin a desiccator which was first evacuated and then filled with nitrogen.The intrinsic viscosity of the resin product was then determined andsuch an intrinsic viscosity value is noted in the examples above as thedegraded intrinsic viscosity.

The percentage broken bonds values indicated in the above examples werecalculated by the use of the following equation:

Percent Broken Bonds:

The value of K and a may be found in the literature, such as Conix, A.,MakromoL, Chemie 26, p. 226 (1958), wherein K=0.00021 and a=0.82. V inthe above formula is the degraded or final intrinsic viscosity value andV is the original or initial intrinsic viscosity value.

All of the intrinsic viscosity determinations of the polyester resinproducts produced in the above examples were determined in a 60% phenoland 40% tetrachloro' ethane solution, wt./Wt., at 30 C., according toconven tional laboratory procedure.

The results in the above examples indicate that the present additives,when added to saturated linear polyester resins, act to stabilize orreduce the degradation effects of higher temperatures upon suchpolyester resins. The change in intrinsic viscosity or the differencebetween the original intrinsic viscosity and the degraded intrinsicviscosity is a direct measure of the heat stabilizing effect that thepresent thermal stabilizers have upon polyester resins and can bereadily calculated from the above results.

When the control above, Example II, is compared with the correspondingExample III wherein the same catalyst systems were used, but With theaddition of a thermal stabilizer of the present invention, it canreadily be seen from the intrinsic viscosity values and the per centagebroken bonds values that the present stabilizers act to limit the amountof degradation that takes place when polyester resin products areexposed to elevated temperatures for prolonged periods of time.

The present invention has been illustrated with particular respect tothe stabilization of polyethylene terephthalate. However, the presentthermal stabilizers are also effective in stabilizing any saturatedlinear polyesters and copolyesters; for example, those derived fromdicarboxylic acids, such as isophthalic acid, and4,4-diphenyldicarboxylic acid, or ester derivatives thereof, andsuitable diols, such as glycols of the series HO(CH OH, where n is 2 to10.

It will be apparent that various different embodiments can be madepracticing this invention without departing from the spirit and scopethereof, and therefore, it is not intended to be limited, except asindicated in the appended claims.

We claim:

1. A stabilized polyester composition comprising a saturated linearpolyester containing a stabilizing amount of a thermal stabilizerselected from those represented by the formula wherein R and R are loweralkyl radicals having from 1 to 6 carbon atoms.

2. The composition of claim 1 wherein the polyester is polyethyleneterephthalate.

3. The composition of claim 1 containing from about 0.01% to about 0.5%,by weight, of the thermal stabilizer, based on the weight of thesaturated linear polyester.

4. The composition of claim 1 wherein the thermal stabilizer is4,4'-tetramethyldiaminobenzophenone.

5. The composition of claim 1 wherein the thermal stabilizer is4,4-tetraamyldiaminobenzophenone.

6. The composition of claim 1 wherein the thermal stabilizer is4,4-tetrapropyldiaminobenzophenone.

References Cited UNITED STATES PATENTS 3,206,428 9/1965 Stanley 26045.93,215,759 11/1965 Miliomis et a1 26045.9 3,380,961 4/1968 Dressler eta1. 26045.9

HOSEA E. TAYLOR, JR., Primary Examiner U.S. Cl. X.R. 260570 UNITEDSTATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 510, 150Dated May 5, 1970 Inventor(s) Mary J. Stewart and Otto K. Carlson It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Column 2, line 12, add a comma after the word-tetramethyldiaminobenzophenone" Column 3, line 5 4, change "10" to lOSIGNED AND SEALED AUG 4 1970 Edward 11. mm I E m MIL m u. IYII Amng 0mmComissionar of Patents FORM podoso (o-69) USCOMM-DC GOING-P69 R u sGOVEINHENY Panama orrlct nu OJi-s3l

